In the step of manufacturing semiconductor devices, a substrate processing apparatus of performing processing such as nitridation, oxidation, and annealing by heating the substrate is adopted. The substrate processing apparatus described above has, for example, a substrate support unit provided in a process chamber for processing a substrate and supporting the substrate, and a heating unit for heating the substrate, in which the substrate loaded into the process chamber is placed on the substrate support unit and the substrate is processed while being heated by the heating unit. Such a heating unit is sometimes provided, for example, in the substrate support unit or in the upper portion of the process chamber.